Protecting the Body

The human body is a fascinating “system of systems The human body is a fascinating “system of systems.” All of these systems must work together to keep the body operating properly. Most of the time they work well and the body functions as it should. There are, however, environmental conditions and other organisms that can negatively affect how the body functions. Micro-organisms, such as bacteria, that cause diseases are referred to as pathogens. Pathogen = any micro-organism that causes a disease

If pathogens are able to enter the body, they either interfere directly with cells or tissues, produce toxins (poisonous chemicals) that can affect the normal functioning of the body. Fortunately, the body has developed a number of ways to defend itself from invasion by foreign organisms and their toxins.

The Primary Defence System

The body’s first line of defence is the skin its function is to keep foreign invaders outside the body it cannot normally be penetrated by bacteria or viruses unless it is broken the skin produces natural acidic oils and sweat that prevents micro-organisms from growing

Did you know... That the skin is the largest organ of the body with a surface area of about 2 m2. The top layer of skin cells is constantly being replaced by new cells, so you have an entirely new skin about every month!

Where the skin leads to the inside of the body, such as in the mouth, nose, eye, and ears, the body has other physical barriers that prevents invaders from entering. Hair tiny hairs filter out dust, dirt, and micro-organisms that are in the air Ear Wax waxy material that traps any foreign particles and micro-organisms that enter

Mucus Found in the mouth, nose, and throat Sticky substance that acts like flypaper Removed by coughing or swallowing 4.Tears Contain a special chemical that kills bacteria Gastric Juices Micro-organisms that sneak past the throat will be destroyed by the strong acid in the stomach

Did you know... Men have more nose hair than women That not all people’s ear wax is the same. Ear wax can be gray, yellow, pumpkin-coloured, or brown. It can also be moist or dry In a year, you are likely to shed about 4 L of tears When you sneeze, the air (and mucus) inside your nose hurtles out at a speed of over 100km/hr You recycle about 1 L of mucus per day by swallowing

The Secondary Defence System

The body’s second line of defence are the white blood cells The body’s second line of defence are the white blood cells. When invading organisms enter the body through a break in the skin, special white blood cells move from the bloodstream to the injured area. These white blood cells detect, capture, and destroy invading organisms just like lysosomes. Lets take a look at how white blood cells work…

Invaders release a chemical that signals the Secondary Defence System This chemical signal causes increased blood flow to the injured area and attracts special white blood cells

The white blood cells engulf and digest the invaders

The body can then heal the tissues in the injured area

The remaining fragments of dead white blood cells and digested invaders are called pus. The presence of pus is a sure sign that the second line of defence is working.

The Tertiary Defence System

Although the two lines of defence are generally successful in protecting the body, they are not always able to stop the invasion. For example, micro-organisms can enter the body in food or water (e.g. E. Coli). They can also be transmitted by insect bites (e.g. Malaria & West Nile virus). When a pathogen does get past the first two lines of defence, the body’s tertiary defence system (the Immune System) is called into action.

all foreign organisms produce a chemical called an antigen this antigen causes the production of a specific antibody that attaches only to this antigen

toxins attach to receptor sites on cells and interfere with normal functions antibodies also attack toxins preventing them from attaching to the cell

The use of antibodies to fight a pathogen is called an immune response The use of antibodies to fight a pathogen is called an immune response. In many cases, the first exposure to a pathogen causes the body to produce its own antibodies, which protect the body against any future attacks by the same pathogen. In other cases, temporary or permanent immunity is achieved by vaccination. Vaccine = an old or weakened version of a pathogen